How to use the concrete volume calculator
This calculator helps you calculate the concrete volume and bag quantity for a rectangular pour. It is intended for quantity takeoffs, early budgets and checks against a measured schedule. Start with the dimensions or quantities for one clearly defined item of work. Enter values in the units shown beside each field; millimetres and metres are not interchangeable.
Dimensions describe one rectangular solid. Imperial inputs are in feet. Bag yield is editable: 0.012 m³ for a 25 kg bag and 0.0085 m³ for a 40 lb bag are illustrative defaults, not manufacturer guarantees. No wastage is added.
Worked example
A 6 m × 4 m slab at 0.15 m thick needs 3.6 m³ before wastage. At 0.012 m³ per bag this is 300 bags.
Before you order
Compare the result with your drawings and supplier information. Keep the original net quantity separate from allowances, and round purchasing quantities only at the ordering stage. Check whether delivery, labour and related materials belong elsewhere in your estimate. If the drawing or specification changes, update the inputs and record the revised basis instead of reusing an earlier total.
For the concepts behind this calculation, read Wastage Factor, Aggregate, Concrete Grade.